1. Preheat oven to 425 degrees Fahrenheit. Spray a foil-lined baking sheet with nonstick spray.
2. Slice onions and mushrooms (if using your food processor, use medium pressure). Place on one side of prepared baking sheet and drizzle with olive oil.
3. Place salmon on baking sheet next to vegetables.
4. Drizzle salmon, onions and mushrooms with balsamic vinegar and honey. Season with salt, pepper and basil. Marinate for 15 to 20 minutes.
5. Bake, uncovered, for 15 minutes. Salmon will be nicely browned on the outside, but still juicy inside. Onions and mushrooms will be tender and golden. Serve immediately. You can also serve this at room temperature.